used. This method did not bond the shim stock to 

 concrete for the duration of the test. A second 

 method used epoxy adhesive Hysol EA 934, which was 

 known to maintain a high bond strength when dry- 

 concrete became wet (Ref 18). The strain data still 

 indicated that the brass shim stock was not adhering 

 to the concrete at the higher pressure (or strain) 

 levels. The third method used Hysol adhesive again, 

 but this time extra attention was paid to roughening 

 the brass surface, deeply roughening the concrete 

 surface (by grinding with silicon carbide grit) and, 

 when applying the gage, embedding the edges of the 

 brass shim stock in a thick bead of epoxy around the 

 periphery. These additional steps also did not solve 

 the problem. The fourth method was to try steel shim 

 stock, instead of brass, and to use the procedures 

 mentioned previously. At the same time, weldable 

 gages were tried. None of these systems was success- 

 ful; attempts at strain gaging were terminated. The 

 deflectometer data were excellent, and additional 

 potentiometers per test were used. 



Television Camera . A closed-circuit television camera was installed 

 at the top of each specimen. The video tape system recorded implo- 

 sion. Although the frames per second rate did not permit detailed 

 study of the failure zone, the circumferential location of failure could 

 usually be defined and an interesting sequence of failure was recorded, 

 including the sound of implosion. "■ 



High-Speed Camera . A high-speed motion picture camera was 

 installed at the top of the specimens . It was hoped that a failure 

 sequence could be filmed. The camera speed was initially set at 200 

 frames/sec which permitted 40 seconds of film time. The speed could 



47 



